In magnetic tapes for audio, video or computer purposes, in general, there is recently an increasing demand for high-density recording, so that conventional Co-containing magnetic iron oxides are being more finely divided. Attention is also being paid to the thin-film type magnetic recording media of ferromagnetic metals, which rely upon ferromagnetic alloy powders, or are formed by the vapor deposition techniques such as vacuum deposition, sputtering and ion plating, said media being now put to practical use.
In such audio, video or computer magnetic tapes, the magnetic layers are finished to a smooth surface to improve the sensitivity (especially the output in a high-frequency range). In coating type magnetic layers, on the other hand, the content of pulverulent bodies other than ferromagnetic powders is reduced as much as possible so as to increase the degree of packing. Thus, the resulting magnetic layers contain a reduced or limited amount of carbon black or the like.
For that reason, in some cases, no improvement might be introduced in running characteristics with conventional backing layers with a smooth surface, the irregularity of which is transferred to the magnetic layers to a lesser extent, and which are composed only of inorganic powders and binders.
In recent years, the total thickness of magnetic tapes tends to be reduced as much as possible, and is now in most cases made no higher than about 20 microns. This is accompanied by a reduction in the thickness of the associated backing layers, and often causes that they are coated in a thickness of no higher than 2 microns. Thus, the reductions in the total thickness of magnetic tapes are entrained by a drop in the strength thereof, and have adverse influences upon running characteristics, running durability, take-up characteristics, output variations, etc. due to static electricity.